Here's a good question, How often should you clean your bow, and what indicates a bow needs cleaning? Does the make of rosin effect this?
Does Alcohol leave a residue and will this effect applying rosin?
Will the age of your rosin make a difference?
With violins there is no fretting over the music.
Clean the bow hair when it looks grungy...... dark near the frog and tip.
I use 91% alcohol and it leaves no residue and cleaning the hair opens the pores and lets the hair take the rosin better.
Rosin doesn't wear out, it may crack but that can be remedied by heating it and sticking it back together, (if it's in pieces) but it doesn't wear out.